Angola Plane Theft and 6 Other Aviation Mysteries

Malaysia Airlines Flight MH370 was carrying 239 passengers, including three Americans, when it mysteriously disappeared off the radar above the South China Sea last Friday.

No distress signals were sent, and no signs have been found of the Boeing 777 airplane, which boasted a near perfect safety record, according to baffled aircraft experts.

Throughout history, numerous incidents of planes vanishing into thin air have captured the attention of the public, aviation experts, and filmmakers alike. Here's a look at some of the most perplexing mysteries, a few of which remain unsolved.

727 Stolen From Angola Airport (2003)

A Boeing 727 took off from Quatro de Fevereiro International Airport in Luanda, Angola, without clearance or a flight plan on May 25, 2003.

The plane, which wasn't painted with an airline logo, hasn't been seen since.

According to the FBI, it was once part of the fleet of a major airline, however it had since been outfitted to carry diesel fuel.

Officials said they believed Ben Charles Padilla, an aviation engineer and pilot, may have been on the plane when it disappeared.

After Air France Flight 447 disappeared over the Atlantic Ocean en route from Rio de Janeiro to Paris in 2009, the cause of the crash remained shrouded in mystery for many months. In the two weeks following the incident on June 1, some wreckage and bodies of the 228 people aboard were recovered, but it would be two years before the main wreckage of the Airbus 330 and its black box was found.

BEA, the French government's official accident investigators, released a final report in July 2012, after a three-year investigation. The report determined that the crash resulted from a combination of technical failures and oversight by untrained pilots, and detailed a chaotic scenario that unfolded as the plane was flying through a thunderstorm. One of the plane's speed sensors had malfunctioned, sending inaccurate readings to the cockpit. Crew failed to realize the severity of the situation, and put the plane into a devastating stall. The plane fell rapidly from the sky, before pancake-ing into the ocean, according to the report.

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TWA Flight 800 (1996)

Conspiracy theories continue to swirl around TWA Flight 800, which exploded in midair off the coast of Long Island, N.Y., in 1996.

A theory that the Paris-bound flight was taken down by a missile amid a federal government cover-up, was one of several that emerged in the months after the crash that killed 230 people on board. Other theories included the belief that a bomb had exploded or a meteor strike downed the Boeing 747-100.

Those claims were all vehemently denied by the FBI and National Transportation Safety Board (NTSB) investigators who spent four years looking into the cause of the crash. In their final report, investigators determined that defective wiring caused a spark that lit up the plane's fuel tank, just 12 minutes after it departed from John F. Kennedy International Airport.

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USAir Flight 427 (1994)

What would have been a short domestic flight from Chicago's O'Hare International Airport to Pittsburgh turned into a scene of carnage as USAir Flight 427 and all 132 people on board plummeted to the ground at speeds approaching 300 mph.

The horrific crash occurred 10 minutes before the plane's scheduled arrival in Pittsburgh on Sept. 8, 1994, but it took officials another four years to finally determine the cause. The results of the investigation finally revealed that a defect in the rudder of the Boeing 737-3B7 caused the experienced pilots to lose control of the plane.

Flying Tiger Flight 739 (1962)

More than 50 years after U.S. military chartered Flying Tiger Flight 793 vanished without a trace, the Super Constellation L-1049 plane is still missing.

It was reportedly a fine and clear day across the Philippine Sea on March 15, 1962, when the plane, transporting soldiers and supplies from California to Saigon, Vietnam, went missing after stopping to refuel in Guam. No distress calls were made and all 107 people aboard were presumed dead, authorities said at the time. Numerous searches by the military failed to turn up any evidence of the airliner, nor the cause of its disappearance.

Pan Am Flight 7 (1957)

On Nov. 8, 1957, Pan Am Flight 7 was en route from San Francisco to Hawaii, when it vanished in the Pacific Ocean. The Boeing 337 plane wreckage was found a week later by the Navy aircraft carrier Philippine Sea, which spotted bodies and plane debris floating off course in the ocean northeast of Honolulu.

The crash, which killed 44 people, has never been definitively determined. The mystery was exacerbated by the fact that no distress signals were sent and toxicology reports revealed higher than normal carbon monoxide levels in the bodies of recovered passengers.